The Components in the System Unit, Chapter 3

1. The Components in the System Unit, Chapter 3 ITSC 1401 Instructor: Glenda H. Easter

2. Objectives • Identify the components in the system unit and explain their functions. • Explain how the CPU uses the four steps of a machine cycle to process data. • Compare and contrast various microprocessors on the market today. • Define a bit and describe how a series of bits are used to represent data.

3. Objectives • Identify the components in the system unit and explain their functions. • Explain how the CPU uses the four steps of a machine cycle to process data. • Compare and contrast various microprocessors on the market today. • Define a bit and describe how a series of bits are used to represent data.

4. Objectives (Continued) • Differentiate between the various types of memory. • Describe the types of expansion slots and expansion cards in the system unit. • Explain the difference between a serial and a parallel port. • Describe how buses contribute to a computer’s processing speed.

5. Overview of This Chapter • This chapter presents the components in the system unit, describes how memory stores data, instructions, and information, and discusses the sequence of operations that occur when a computer executes an instruction.

6. The System Unit • The system unit is a box-like case that houses the electronic components of the computer that are used to process data. The system unit, exposed

7. The Motherboard or the System Board • CPU • Memory • Expansion Slots • Ports

8. The Motherboard • This is also called the system board. It contains the CPU and some memory chips. • The motherboard is the main circuit board of a computer. • The motherboard has expansion slots designed for: Expansion cards Ports to enable the computer to communicate.

9. The Most Important Chip:The CPU • The motherboard in the system unit contains many different types of chips. • Of these, one of the most important is the central processing unit (CPU).

10. CPU (The Brain of the Computer) Two parts: • ALU (Arithmetic/Logic Unit) • CU (Control Unit)

11. Central Processing Unit • The CPU is the part of the computer that runs the program or executes program instructions. It is also known as the processor. • The CPU is located on a single electronic component called the microprocessor chip. • The chip is housed in the system unit or system cabinet.

12. Parts of the CPU • There are two parts of the Central Processing Unit: The control unit The arithmetic logic unit • The control unit tells the rest of the computer how to carry out a program’s instructions.

13. The Control Unit • The control unit contains the microprocessor, memory, and storage devices. • It directs the control signals between the CPU and input and output devices. • The CPU directs movement of electronic signals between memory and the ALU.

14. The Control Unit • The Control Unit controls the flow of data intoand from the Central ProcessingUnit

15. Functions of the Control Unit • The control unit directs and coordinates most of the operations in the computer. • For every instruction, the control unit repeats a set of four basic operations: • “Fetching” an instruction • Decoding the instruction • Executing the instruction • Storing the result, when necessary • These four operations comprise the machine cycle or instruction cycle.

16. Machine Cycle or Instruction Cycle • Fetching: The process of obtaining a program instruction or data from memory. This is called instruction time. • Decoding: Translating the instruction into commands the computer understands. • Executing: Carrying out the commands. This is called execution time • Storing: Writing the result to memory.

17. The Arithmetic-Logic-Unit(ALU) • The ALU is the device that performs fundamental math operations such as addition, subtraction, multiplication, and division. • The ALU also handles logical operations that compare two pieces of data to see if they are equal, less than, or greater than the other.

18. Pipelining • In some instances, the computer only processes a single instruction at a time. When the CPU has to wait until one instruction is complete before starting the next instruction. • With pipelining the CPU begins to execute a second instruction before the first instruction is completed. This results in faster processing.

19. Registers • The computers have additional storage locations in the control unit, and these are called registers. • Registers are high-speed staging areas that hold data and instructions temporarily during processing. • Functions of registers include storing the location where an instruction was fetched, storing an instruction while it is being decoded, storing data while the ALU processes it, and storing the results of a calculation.

20. System Clock • A microprocessor’s speed is determined by two major factors: bus speed  clock speed • The system clock controls how fast instructions are processed and the speed of your system. • The speed is measured in megahertz (MHz).1 megahertz = 1 million beats (cycles) per second. • The speed affects only the CPU and has no effect on peripherals.

21. The System Clock About MHz: the faster the clock, the faster the processing speed. (1 MHz = 1 million clock cycles per second) The Pentium II has 7.5 million transistors, more than double the number included on the original Pentium chip. It can operate from 233 MHz to 400 MHz and beyond.

22. Microprocessor Chips • Intel • 486 • 586 • Motorola • 68030 • 68040 • DEC

23. Processing Chip • In a microcomputer, the central processing unit is contained on a single silicon chip. This is called the microprocessor chip. • Processing chips include: Intel Chips used by IBM Motorola Chips used by Macintosh Digital Equipment Corporation Chips used by minicomputers, mainframes, and supercomputers.

24. Microprocessor Comparison • A microprocessor often is identified by its model name or model number. • Intel leads the manufacturers of processors. • After learning the CPU numbers could not be trademarked and protected from use by competitors, Intel decided to identify their microprocessors with names, not numbers.

25. Microprocessor Comparison(Continued) • Pentium Processors is the number one leader in microprocessor chips. • Celetron is designed for less expensive PCs • Xeon and Itanium are geared toward workstations and servers. • Motorola microprocessor which is found in Apple Macintosh and Power Macintosh systems. • Alpha microprocessor was developed by Digital Equipment Corporation is used primarily in workstations and high-end servers.

26. Microprocessor Comparison(Continued) • A new type of microprocessor called an integrated CPU, combines functions of a CPU, memory, and a graphics card on a single chip.

27. Processor Installation and Upgrades • Processor chips are inserted into an opening or socket on the motherboard. • Most computers today have a ZIF socket which is designed to facilitate the installation and removal of processor chips.

28. CPU Manufacturers • Intel • Motorola • AMD • Cyrix

29. CPU Models • 8086 1978 • 8088 1979 • 80286 1982 • 80386 1985 • 80486 1989 • Pentium 1993 • Pentium Pro 1995 • Pentium II 1997 • Pentium III 1999

30. Processor Upgrades • Processor upgrades take one of three forms: • Chip for Chip Upgrade where the existing chip is replaced with a new one. • Piggyback Upgrade: A new processor chip is stacked on top of the old one. • Daughterboard Upgrade: A daughterboard upgrade is a small circuit board that plugs into the motherboard. It often adds additional capabilities to the motherboard.

31. Heat Sinks and Heat Pipes • Newer processor chips generate a lot of heat which could cause the chip to burn up. • A heat sink is a small ceramic or metal component with fins on its surface that is designed to absorb and ventilate heat produced by the electrical components. • A heat sink consumes a lot of room; therefore, a smaller device called a heat pipe is used to cool laptop computers.

32. Data Representation • Computers can operate in only two states: on and off. The on state is represented by one (1). The off state is represented by zero (0). • Computers work totally with data that has been encoded with 0 and 1 and is therefore called the binary system.

33. Computers Represent Data With Electrical Switches = 1 On-off circuits are simple and are not prone to errors. = 0 0 1 0 0 1 0 0 0 One byte is made up of 8 bits. (binary 01001000 = decimal 72) (ASCII 01001000 = the letter “H”)

34. Three Principal Binary Coding Schemes • ASCII • EBCDIC • Unicode • Each scheme groups binary numbers in a different way; therefore, when files are used or shared by different computers or applications, they must use the same coding scheme.

35. ASCII (American Standard Code for Information Interchange Code) • ASCII is the most widely used binary code for microcomputers. • It is the code used on personal computers. • Some application programs attach special meanings to certain ASCII codes.

36. ASCII(Continued) • These designated purposes include formatting such as boldface and italics. • For this reason, one program cannot read data created in another program unless it is translated to the other program’s codes.

37. EBCDIC (Extended Binary Coded Decimal Exchange Code) • EBCDIC was developed by IBM and used on many IBM and other kinds of computers. • It is almost an industry standard for large computers, especially mainframes. • Although EBCDIC is slowly dying out, a great deal of data stored on tape use EBCDIC character set, so the need to have programs convert from EBCDIC to ASCII is not going away.

38. EBCDIC versus ASCII • EBCDIC was always an 8-bit character code, and it could represent 256 characters. • ASCII was initially a 7-bit character code, so ASCII could only represent 128 distinct characters.

39. Unicode • Unicode is a sixteen-bit code designed to support international languages like Chinese and Japanese. • It was developed by Unicode, Inc. with support from Apple, IBM, and Microsoft.

40. A Bit about Bytes • The smallest unit of measure is a nibble. This is one-half of a bit. • Today, both ASCII and EBCDIC use an eight-bit coding system. • ASCII added one bit for parity. • An extra bit, called a parity bit, is automatically added to each character’s code in a computer system.

41. A Parity Bit • A parity bit is used to check for memory or data communication errors. It verifies the validity of data as it passes through the electronic circuitry of the computer components. • A parity bit enables the computer to detect an error, but does not tell the computer how to correct the error.

42. A Parity Bit (Continued) • An even-parity bit system is set to either o or 1 to ensure the number of 1s is even in the byte. • With an odd-parity bit system, the parity bit is set to either 0 or 1 to ensure the number of 1s is odd in the byte.

43. Internal Memory • RAM • Virtual Memory • Cache Memory • ROM

44. Memory • Most computers use memory as scratch pads to hold programs and data in use in the CPU. • The four types of memory are: RAM  Virtual  Cache  ROM

45. The Capacity of Memory • The capacity of memory is measured by the number of characters of data or instructions it can hold. • Before you buy any software package, check to see how much memory it requires to run. • You can add more memory by adding memory chips.

46. Addresses • During the processing cycle, data or instructions are placed in main memory locations called addresses. • Each address location is identified by a unique number that always remain the same. • Although the memory address numbers always stay the same, the contents within the addresses locations are continually changing.

47. RAM (Random-Access Memory) • RAM is the internal storage area of the system unit called memory of primary storage. • RAM holds the program and data that the CPU is presently processing. • RAM is temporary or volatile storage.

48. RAM (Continued) • Data and programs must be loaded into RAM before they can be used by the computer. • RAM’s temporary storage capacity is measured in terms of bytes.

49. Random Access Memory • In RAM, each memory location has an address, just like a post office box. data

50. DRAM and SRAM • Two basic types of RAM exist: • Dynamic RAM (DRAM): This type of RAM must be re-energized constantly or it loses its contents. • Static RAM (SRAM): It is faster and more reliable than any form of DRAM. It does not have to re-energized as often as DRAM. • SRAM is much more expensive than DRAM.